The invention relates to dielectric materials comprising films of Rxe2x80x94Gexe2x80x94Tixe2x80x94O where R is selected from Zr and Hf, and to methods of making the same. The invention is particularly useful in silicon-chip integrated circuit devices such as a capacitor of a dynamic random access memory (DRAM) device.
As microelectronic circuits have become increasingly integrated, the demand for smaller components has become stronger. The quest for miniaturization is particularly ardent with regard to DRAM cell devices. The migration of integrated circuits to smaller feature sizes is motivating interest in the development of thin film dielectrics having dielectric constants (∈) greater than those of previously used materials. There are many performance constraints on the materials that may be used, however. For instance, DRAM storage capacitors require a capacitance of greater than about 20 fF. See, e.g., El-Kareh et al., xe2x80x9cThe Evolution of DRAM Cell Technology,xe2x80x9d Solid STATE TECH. (May 1997), at pp. 89-101.
Typically, films of a-SiOx have been used as a dielectric material in DRAM capacitors or capacitors of integrated-circuit devices. As the cell size has shrunk, designers have resorted to films of a-SiOx that are extremely thin or non-planar, but these films are problematic as they exhibit a decreased reliability due to finite breakdown fields or have other attendant problems such as step coverage and conformality. Thus, efforts have been directed toward developing new dielectric materials that can be substituted for a-SiOx films, thus avoiding the inherent limitations of those films.
Attention has been focused on Ta2O5, TiO2, and (Ba,Sr)TiO3, the barium strontium titanate composites being referred to as BST. Each of these offers advantages and disadvantages. For example, titanium-oxide (TiO2) has a high dielectric constant (∈xcx9c80), making films of TiO2 potentially useful in various roles in integrated circuits, such as metal oxide semiconductor or memory capacitors, gate oxides, and other circuit elements. See, e.g., Y. H. Lee et al., xe2x80x9cPlasma Enhanced Chemical Vapor Deposition of TiO2 In Microwave-Radio Frequency Hybrid Plasma Reactor,xe2x80x9d J. VAC. SCI. TECH. A 13 (3) 1995, at p. 596; J. Yan et al., xe2x80x9cStructural and Electrical Characterization of TiO2 Grown From Titanium Tetrakis-Isopropoxide (TTIEP) and TTIP/H2O Ambients,xe2x80x9d J. VAC. SCI. TECH. B 14 (3) 1996, at p. 1706.
However, crystalline TiO2 (x-TiO2) films have demonstrated high leakage currents (low breakdown fields), which adversely influences the operation of DRAM circuits and impacts on the reliability of the capacitors. (Ba,Sr)TiO3 requires high deposition and processing temperatures, making it undesirable for many purposes. Amorphous Ta2O5 (a-TiO2) is more straightforward to process than Ba,Sr)TiO3, does not require high-temperature processing, and has a low leakage current. However, it has a relatively low dielectric constant (∈xcx9c23), so it is unlikely to provide a long-term solution. Thus, those involved in the field of dielectric materials continue to search for new materials having high dielectric constants for use in capacitors and microelectronics.
A relative decrease in the dielectric constant for amorphous titanium-oxide-based films is reported in O. Nakagawara et al., xe2x80x9cElectrical Properties of (Zr,Sn)TiO4 Dielectric Thin Film Prepared by Pulsed Laser Deposition,xe2x80x9d J. AAPPL. PHYS. 80, 388 (1996) (xe2x80x9cNakagawaraxe2x80x9d), which attribute this decrease to the ionic polarizability of the materials. Nevertheless, the applicants have studied amorphous films of titanium-oxide-based materials in the continuing search for new dielectric materials. Amorphous titanium-oxide-based compositions exhibiting useful properties as dielectrics are described in U.S. Pat. No. 5,912,797, titled xe2x80x9cDielectric Materials of Amorphous Compositions and Devices Employing Same,xe2x80x9d issued Jun. 15, 1999 to the inventors herein, Schneemeyer and VanDover, and assigned to Lucent Technologies, the assignee herein, which is hereby incorporated by reference. The ""797 patent describes amorphous titanium-oxide films containing both tin (Sn), and either hafnium (Hf) or zirconium (Zr). The materials of the ""797 patent have high dielectric constants of 50-70 and breakdown fields of 4 MV/cm with films of 40-50 nm in thickness. The materials were obtained using off-axis sputtering using three independently controlled guns. Although these new amorphous films have excellent dielectric properties, other constraints must be met to incorporate them within semiconductor products. For example, an etching process, preferably a plasma etching process, must be developed so that the films can be patterned. While titanium may be readily etched because it forms a volatile chloride, the etching behaviors of tin and zirconium are not as well known.
As may be appreciated, those concerned with the development of integrated circuit devices continually search for new materials and methods for improving device performance as the circuit size becomes progressively smaller. This search includes the discovery of new dielectric materials compatible for use in DRAM cells or silicon-chip integrated circuit devices having high dielectric constants and large breakdown fields (low leakage currents), that are relatively uncomplicated to process, and are capable of being readily etched.
The invention relates to a dielectric film comprising Rxe2x80x94Gexe2x80x94Tixe2x80x94O, wherein R is selected from zirconium and hafnium. The dielectric film is preferably an amorphous composition having the formula Rxxe2x80x94Geyxe2x80x94Tizxe2x80x94Ow, where 0.05xe2x89xa7xxe2x89xa61, 0.05xe2x89xa7yxe2x89xa61, 0.1xe2x89xa7zxe2x89xa61, and 1xe2x89xa7wxe2x89xa62, and x+y+z≅1 and more preferably, where 0.15xe2x89xa7xxe2x89xa60.7, 0.05xe2x89xa7yxe2x89xa60.3, 0.25xe2x89xa7zxe2x89xa60.7, and 1.95xe2x89xa7wxe2x89xa62.05. The thickness of the film and values for x, y, z and w may be selected so that a thin film (xcx9c80-100 nm) of the material will exhibit a dielectric constant of about 40 or higher, leakage current of less than 10xe2x88x926 A/cm2, and a figure of merit of about 18 xcexcC/cm2 or higher.